Emergency Lighting Device For Operating A Light Source, In Particular An LED

ABSTRACT

An emergency lighting device ( 1 ) for operating a light source, in particular an LED, incorporates an energy storage unit ( 4 ), a charging circuit ( 3 ) to be supplied with mains supply voltage (U in ) for charging the energy storage unit ( 4 ) during a charging operation, wherein the charging circuit ( 3 ) has potential isolation, and a driver circuit ( 5 ) supplied by the energy storage unit ( 4 ) during operation of the emergency light, for operating the light source. A control unit ( 2 ) is further provided that is designed to monitor the state of the mains supply voltage (U in ) during the charging operation, and to activate emergency operation upon detecting an emergency state, wherein the control unit ( 2 ) determines the state of the mains supply voltage (U in ) from operating parameters of the emergency lighting device ( 1 ) measured on the output side of the charging circuit ( 3 ).

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an emergency lighting device intendedfor operating a light source, in particular an LED.

BRIEF SUMMARY OF THE INVENTION

Emergency lighting devices are essential for realizing, in largerbuildings or complexes, lighting systems that provide adequate lightingeven in the event of failure of the general mains power supply.Evacuation or assistance measures can be performed safely only ifcertain relevant parts or areas of buildings continue to be illuminatedin the event of failure of the electric power supply. Accordingly, suchemergency lighting devices are used, in particular, for illuminatingescape routes and the like.

Emergency lighting devices of the generic type accordingly have, as acentral element, an energy storage unit, in particular a battery oraccumulator, that is charged by the general mains supply voltage duringa normal, or charging, operation. Provided for this purpose is acharging circuit that is connected on the input side to the mains supplyvoltage and, during the charging operation, permanently supplies energyto the energy storage unit, which stores this energy. Changeover toemergency lighting operation, in which the light source is activated andoperated, for which purpose—insofar as necessary—the energy provided bythe energy storage unit is used, is effected only in the event of theoccurrence of an emergency state, which is usually identifiedautomatically by such devices, through monitoring of the mains supplyvoltage. Since the storage capacity of the energy storage unit isclearly limited, light sources that consume relatively little energy areused by preference. Accordingly, such emergency lighting devices arepreferably equipped with gas discharge lamps, in particular fluorescenttubes. Increasingly, however, light sources in the form oflight-emitting semiconductors, in particular LEDs, are being used, sincethese light sources also have high efficiency and, accordingly, can beused in an energy-saving manner.

The monitoring of the mains supply voltage, which is therefore performedto enable emergency lighting operation to be initiated in a timelymanner, is usually effected by a control unit that evaluates signalssupplied to it and assesses the state of the mains supply voltage on thebasis of these signals. In the case of known circuits, the mains supplyvoltage itself is measured in an obvious manner. This then gives rise tothe problem, however, that the sensors for determining the state of themains supply voltage are at mains potential, and must be galvanicallyisolated from the other circuit areas of the emergency-lighting devicethat are at the voltage level of the energy storage unit or LED. Thepotential isolation required for this purpose is not only expensive, butmoreover also occupies a relatively large amount of space in theemergency lighting device.

BRIEF SUMMARY OF THE INVENTION

The invention concerns an improved concept for an emergency lightingdevice in which the disadvantages described above are avoided.

Core concept of the present invention is that, in contrast to knownsolutions, the mains supply voltage is now monitored only in an indirectmanner in order to initiate emergency lighting operation if necessary.For this purpose, only measurement values at the potential of the energystorage unit or LED are acquired, and the state of the mains supplyvoltage is deduced on the basis of these measurement values, with theaid of further information.

There is accordingly proposed according to the invention an emergencylighting device for operating a light source, in particular an LED, theemergency lighting device having:

-   -   an energy storage unit,    -   a charging circuit to be supplied with a mains supply voltage        for charging the energy storage unit during a charging operation        of the emergency lighting device, the charging circuit having        potential isolation, and    -   a driver circuit supplied by the energy storage unit during        operation of the emergency light, for operating the light        source,        the device further having a control unit that is designed to        monitor the state of the mains supply voltage during the        charging operation, and to activate emergency lighting operation        upon identifying an emergency state. In this case, according to        the invention provision is made whereby the control unit        determines the state of the mains supply voltage on the basis of        operating quantities of the emergency lighting device that are        measured on the output side of the charging circuit.

It is ensured, through the measures according to the invention, that anemergency state affecting the voltage supply can still be reliablyidentified and emergency lighting operation can be initiatedaccordingly. At the same time, however, the necessary galvanic isolationbetween the means for monitoring the mains supply voltage and the othercomponents of the emergency lighting device has been omitted, so thatthe device, taken as a whole, can be realized in a less expensive andmore compact manner.

Preferably, the charging circuit has a controllable switch and atransformer, the charging circuit being able to be constituted, inparticular, by a so-called flyback converter. The controllable switch isactivated by the control unit of the emergency lighting device, theactivation in this case being able to be effected via an optocoupler.

The state of the mains supply voltage is now determined, in particular,with account being taken of the duty cycle, selected by the controlunit, for activating the switch of the flyback converter or of thecharging circuit. The secondary voltage of the flyback converter or, inthe case of other switched-mode power supply topologies, the chargingpower for the energy storage unit is further taken into account for thispurpose. This charging power can be can be easily determined by thecontrol unit during the charging operation, i.e. with the light sourceswitched off, since the values to be measured for this purpose, namely,voltage and current of the energy storage circuit, relate to the samebasic potential that the further components of the emergency lightingdevice are also at. The same also applies to the secondary voltage to bemeasured in the case of use of the flyback converter. In both cases,therefore, the galvanic isolation, between the measuring devices and thecontrol unit, that is necessary in the case of the prior art can beomitted.

A further advantageous development of the present invention relates tothe measures for operating the light source, in particular the LED,during emergency lighting operation. For this purpose, the drivercircuit is preferably realized as a switching regulator and accordinglyhas a further controllable switch that, in turn, is activated by thecontrol unit. The activation of the switch in this case is such that thelight source can be operated with a constant power or constant currentirrespective of the state of charge of the energy storage unit. Thismeasure is of particular importance, since the power of the energystorage unit clearly declines over time, which, however, should notaffect the light intensity of the emergency lighting device.

In the case of an LED being used as a light source, in order to renderpossible the desired power regulation it would accordingly be obvious,in turn, to measure the actual diode current that determines thelighting power. According to a particularly advantageous development ofthe present invention, however, provision is made whereby there is nomeasurement of the diode current and, instead, the current, or thepower, of the light source is measured or estimated indirectly on thebasis of other parameters. In particular, preferably only the voltagepresent at the light source is determined, and the diode current is thendeduced from further information, the power loss of the driver circuit,in particular, being taken into account in this case. The power of thelight source can then be determined, without direct measurement of thediode current, by means of previously determined matching tables storedin the control unit, such that an almost constant lighting power can beset by the control unit. The regulation of the lighting power in thiscase is effected, in particular, through corresponding clocking of thecontrollable switch of the driver circuit, since in this way the powerwith which the light source is operated can be set in a very simple andelegant manner.

Moreover, this particular measure, for operating the light source withan almost constant power, with no direct measurement of the current, canalso be used independently of the concept according to the invention,described at the beginning, of indirect monitoring of the mains powersupply.

BRIEF DESCRIPTION OF THE FIGURES

The invention is to be explained more fully in the following withreference to the accompanying drawing, wherein:

FIG. 1 shows, in schematic form, the circuit diagram of a firstembodiment of an emergency lighting device according to the invention;

FIG. 2 shows a second embodiment of an emergency lighting device;

FIG. 3 shows a graph for determining the mains supply voltage on thebasis of operating parameters measured on the output side of thecharging circuit, and

FIG. 4 shows a graph for determining the secondary power of the chargingcircuit, which secondary power is taken into account for indirectdetermination of the light source power.

DETAILED DESCRIPTION OF THE INVENTION

In the embodiment represented, the emergency lighting device accordingto the invention, which in FIG. 1 is represented in a simplified mannerand denoted by the reference 1, is intended for operation of an LED asan emergency lighting source. The emergency lighting device 1 isconnected, on the input side, to an electric power supply networkproviding a mains supply voltage U_(in), and comprises, as essentialcomponents, a control unit 2, a charging circuit 3, an energy storageunit 4 in the form of a battery or accumulator, and a driver circuit 5.In the represented first embodiment, the charging circuit 3 isconstituted by a so-called flyback converter that, on the one hand, hasa transformer T comprising a primary winding n1 and a secondary windingn2 and, on the other hand, has a controllable switch S1. In knownmanner, the energy provided by the mains supply voltage U_(in) can betransferred to the secondary side of the flyback converter 3 throughappropriate alternating opening and closing of the switch S1, and usedfor charging the energy storage unit 4. The transfer of energy in thiscase is effected when the switch S1 is in the open state, a diode D₁additionally being provided for this purpose on the output side of theflyback converter 3. Such flyback circuits are used in many instances insuch emergency lighting devices, owing to their simple structure andtheir reliable functioning.

The activation of the controllable switch S1 is effected by the controlunit 2 of the emergency lighting device, the activation being effected,in particular, with galvanic isolation, via an optocoupler 6. Thecontrol unit 2 in this case activates the switch S1 alternately, theso-called duty cycle D1 for the switching operation of the switch S1being calculated as follows:

D1=t _(on1)/(T−t _(on1))

t_(on1) in this case corresponds to the on-time of the switch, while Tdenotes the total duration of a complete switching cycle for the switchS1.

It is also conceivable for the activation of S1 to be a ‘freeoscillator’, and for the natural frequency of the ‘free oscillator’ tobe influenced by the optocoupler 6 via the duty cycle.

During a charging operation of the emergency lighting device 1, usuallyit is exclusively the charging circuit 3 that is active, for the purposeof continually charging the battery 4. An emergency lighting operation,in which the driver circuit 5 is used to activate the LED, is initiatedonly in the event of an emergency state, which is characterized, inparticular, by deviations in the power supply voltage U_(in) frompredetermined setpoint values. For this purpose, the driver circuit 5realized as a switching regulator has a further controllable switch S2,an inductor L and a diode D₂. Through alternating activation of theswitch S2 by the control unit 2, the LED is provided with a current bymeans of which this LED is operated. The pulse duty factor with whichthe switch S2 is activated by the control unit 2 can be varied in thiscase in order to set the level of the current supplied to the LED, andthereby the power with which the LED is operated. In this way it can beensured, in a very elegant manner, that, even in the case of fluctuatingbattery power, the LED is nevertheless operated with constantbrightness.

A first essential function of the emergency lighting device 1 thereforeconsists in identifying, through assessment of the mains supply voltageU_(in), whether an emergency state exists, in order to initiateemergency lighting operation if necessary. There has been known hithertofor this purpose the practice of directly determining the value of theinput voltage U_(in) for the charging circuit 3, this, however, beingassociated with disadvantages, for the reasons previously stated.

According to the present invention, therefore, there is now no directmeasurement of the mains supply voltage U_(in). Instead, provision ismade for indirectly determining this mains supply voltage. Inparticular, provision is made whereby only magnitudes of operatingparameters of the emergency lighting device 1 are measured on thesecondary side of the charging circuit 3.

In the case of the first embodiment according to FIG. 1, the voltageU_(flb2) present on the secondary side of the isolating transformer orflyback converter 3 is measured for this purpose, for which, inparticular, no galvanic isolation is required, since this quantity is atthe same reference potential as the control unit 2 that evaluates themeasurement value. If the level of this secondary voltage U_(flb2) isthen known, the level of the input voltage U_(in) can be deducedtherefrom. This is because, when the switch S1 of the flyback converter3 has been switched on, there is a relationship between input voltageU_(in) and secondary voltage U_(flb2) that is dependent, in particular,on the winding ratio between the two windings n1 and n2 of thetransformer T and on the duty cycle of the switch D1. This relationshipbetween the easily measured secondary voltage U_(flb2) and the inputvoltage U_(in) to be monitored is now stored, in the form of a valuetable, in the control unit 2, so that the latter, after measurement ofthe secondary voltage U_(flb2), can easily determine the level of theinput voltage U_(in) without having to measure this input voltagedirectly. If the control unit 2 now finds that the determined inputvoltage U_(in) lies outside determined setpoint ranges, this indicatesan emergency state, which, in turn, will cause the control unit 2 toinitiate emergency operation.

The described solution thus renders possible very simple but effectivemonitoring of the state of the general electric power supply. Further, aparticular advantage of the embodiment represented in FIG. 1 consists inthat the level of the input voltage U_(in) can be determinedirrespective of whether or not the emergency lighting LED is switchedon. This is because the diode D₁, through its blocking action, effectsisolation between secondary voltage U_(flb2) and battery voltageU_(Bat), so that the activity of the driver circuit 3 does not act uponthe previously described operation of determination of the input voltageU_(in).

A second, somewhat more general embodiment of an emergency lightingdevice according to the invention is represented in FIG. 2. In itsstructure, this device corresponds substantially to the emergencylighting device 1 shown in FIG. 1, but the charging circuit 3 is nowconstituted, not by a flyback converter, but generally by a circuitarrangement having potential isolation and a switch S1 again activatedby the control unit 2.

In the case of this more general embodiment, there is not necessarily aknown relationship between the input voltage U_(in) and the voltage onthe output side of the charging circuit 3. Nevertheless, in this caselikewise, the level of the input voltage U_(in) can be determinedindirectly, but with other operating quantities now being measured forthis purpose.

These are, on the one hand, the battery voltage U_(bat) and, on theother hand, the battery current I_(bat). Both quantities can again bedetermined in a relatively simple manner, i.e. without galvanicisolation, since they are again at the same reference potential as thecontrol unit 2 that evaluates these measurement quantities.

On the basis of these two measurement quantities U_(bat) and I_(bat) andof the known duty cycle D1 for the switch S1 of the charging circuit 3,it is then possible to determine the input voltage U_(in), since thereis a relationship between the latter and the three known quantities.This is illustrated by the graph of FIG. 3, which shows differingcharacteristics of the secondary power P_(flb2) of the charging circuit3 in dependence on the duty cycle D1 for the switch S1. Thesecharacteristics are determined, for example, during production of theemergency lighting device, and are again stored in the form of a tablein the control unit 2. It can be seen that these characteristics arealso dependent, in particular, on the input voltage U_(in). Therefore,if the duty cycle D1 and the secondary power P_(flb2) of the chargingcircuit 3 are then known, the level of the input voltage U_(in) can bededuced, as in the case of the example of FIG. 1.

In the represented example of FIG. 3, therefore, there is determinedthat characteristic with which the known combination, of duty cycle D1and secondary power P_(flb2) of the charging circuit 3, that, with thedriver circuit 5 deactivated, corresponds to the product of batteryvoltage U_(bat) and battery current I_(bat), is in conformity. In thecase of the represented measurement values, for example, this value lieson the characteristic for an input voltage U_(in) of 220 volt, whichcorresponds to a correct state of the general mains supply. However,should the determined value lie on a characteristic corresponding, forexample, to an input voltage U_(in) of 140 volt or 280 volt, the controlunit 2 would in turn interpret this as a fault being present in themains supply, and accordingly initiate an emergency state.

In both embodiments shown, therefore, it can be ascertained reliably andwithout the need for direct measurement of the input voltage U_(in)whether or not the mains supply is satisfactory. However, a limitationin the case of the example of FIG. 2 consists in that the describeddetermination of the input voltage U_(in) is possible only when thedriver circuit 5 is in the off state. In the case of the example of FIG.1, by contrast, this limitation—as already mentioned—does not exist.Fundamentally, however, the control unit 2, in the event ofidentification of a fault, will cause the driver circuit 5 to beactivated and, accordingly, cause the LED to be switched on.

Following activation of the driver circuit 5, the switch S2 can then beactivated at high frequency, in the manner previously described, inorder to operate the LED with the desired power. In order to ensure inthis case that the power of the LED is constant, it would be necessaryto know both the LED voltage U_(led) and the LED current I_(led) forregulation to be rendered possible. According to a particularlyadvantageous development, however, only the LED voltage U_(led) ismeasured, and the current I_(led), or the power P_(led) resultingtherefrom, is determined indirectly by the control unit 2, as is to beexplained more fully in the following.

To enable the diode current I_(led) to be determined indirectly, atleast the quantities battery voltage U_(bat), battery current I_(bat)and—in the case of the example of FIG. 1—secondary voltage U_(flb2) andadditionally the LED voltage U_(led) are now measured. The furtherinformation required for regulating the LED current I_(led) can then becalculated therefrom, for which purpose, however, there is required yetfurther information, which is not acquired through actual-valuemeasurements, but which is stored as value tables in the control unit 2.

The first value table is the information, already mentioned above,regarding the relationship between duty cycle D1, secondary voltageU_(flb2) and input voltage U_(in) in the case of the example of FIG. 1,or between duty cycle D1, battery voltage U_(bat), battery currentI_(bat) and input voltage U_(in) in the case of the more general exampleof FIG. 2. Further, for the purpose of determining the diode current, itis also necessary that the power loss P_(lost) of the driver circuit 5be known, which power loss is dependent on the difference between themeasured LED voltage U_(led) and the likewise measured battery voltageU_(bat), so that the following applies:

P _(lost) =f(U _(led) −U _(bat))

The third required information, finally, is the secondary power P_(flb2)of the charging circuit 3, which is present in the case of an activateddriver circuit and which is a function of the duty cycle D1, the inputvoltage U_(in) and the battery voltage U_(bat). The relationship betweenthese quantities is represented in FIG. 4, where it can be seen that thesecondary power P_(flb2) of the charging circuit 3 is dependentprimarily on the input voltage U_(in) and the duty cycle D1 for theswitch S1, although it can also additionally vary on the basis of thebattery voltage U_(bat).

If the input voltage U_(in) has now been determined (in the case of theexample of FIG. 2, with the driver circuit 5 first switched off ifapplicable) on the basis of the previously described measures, thesecondary power P_(flb2) of the charging circuit 3 can be determined onthe basis of the relationship in FIG. 4, even with the driver circuit 5activated. There are then known, therefore, the measured quantitiesbattery voltage U_(bat), battery current I_(bat), if applicablesecondary voltage U_(flb2) and LED voltage U_(led), the duty cycle D1for the switch S1 set by the control unit, and the further quantities,determined on the basis of the stored value tables, input voltageU_(in), secondary power P_(flb2) of the charging circuit 3 and powerloss P_(lost) of the driver circuit 5.

The knowledge of these quantities, in turn, renders possibledetermination, firstly, of the current I_(flb2) on the secondary side ofthe charging circuit 3 according to the following relationship:

I _(flb2) =P _(flb2) /U _(bat)

Finally, the LED current I_(led) and the LED power P_(led) can also becalculated according to the following equations;

I _(led)=(P _(flb2) −U _(bat) ·I _(bat) −P _(lost))/U _(led)

P _(led) =P _(flb2) −U _(bat) ·I _(bat) −P _(lost)

Both equations apply to the case of the charging circuit 3 continuing tobe active, i.e., whereby at least a certain electric power supply isstill available. This can be the case, for example, if emergencylighting operation has been brought about in another manner. Bycontrast, in the case of the electric power supply failing completelyand emergency lighting operation being maintained solely by the battery,the following simplified equations apply:

I _(led)=(U _(bat) ·I _(bat) −P _(lost))/U _(led)

P _(led) =U _(bat) ·I _(bat) −P _(lost)

Finally, the current actual value of the LED current I_(led) and thecurrent power P_(led) can be determined indirectly, and used forregulation. The corresponding calculations are performed by the controlunit 2.

The advantage of these indirect determinations of the actual valuesnecessary for regulation consists in that it is possible to dispensewith a measurement of an additional operating parameter of the emergencylighting device, which, in turn, results in a further simplification ofthe device as a whole. Since, in this instance, some use can be made ofparameters already determined or measured for the purpose of determiningthe input voltage in any case, this indirect determination of the LEDcurrent therefore constitutes a particularly advantageous development ofthe concept of the indirect determination of the input voltage describedat the beginning. However, a corresponding indirect current and powerdetermination for the light source could also be used in the case ofother devices in which the first concept according to the invention isnot realized. For example, this procedure is appropriate, inter alia, inthe case of emergency lighting devices in which an emergency state canalso be signalled in another manner, as an alternative or in addition tothe monitoring of the electric power supply. Thus, in the case of theemergency lighting device according to the invention, for example, anemergency signal could also be transmitted via a separate control input,e.g. from a fire alarm or another control device, in order to initiateemergency lighting operation through an external signal.

A further development, finally, relates to the previously mentionedvalue tables stored in the control unit, which are necessary forindirect determination of the input voltage and of the diode current.

As has already been mentioned, these value tables can be already storedin the control unit during the production of the emergency lightingdevice. Alternatively, or in addition thereto, however, it would also beconceivable for this information to be entered retroactively or updatedat a later point in time. A digital interface, for example, provided inthe emergency lighting device, could be used for this purpose, whichinterface is usually used for fault signalling and monitoring. New valuetables could then be entered into the control unit with the aid of thisinterface, with the use of an expanded instruction set. This retroactiveentering of new information is appropriate, for example, for specifyingnew setpoint or tolerance values for the input voltage or, also, foradapting the information for determining the non-directly measuredquantities to the connected battery. As a result, therefore, theemergency lighting device can be adapted to new circumstances at anytime in respect of its behaviour.

Taken as a whole, therefore, there is provided by the present inventiona new type of emergency lighting device, which is distinguished by itssimple and inexpensively realized structure and which neverthelessenables an emergency situation to be ascertained through monitoring ofthe general mains supply. Moreover, a constant light output beyond theduration of an emergency operation is ensured through the advantageousregulation of the diode current.

1. An emergency lighting device for operating a light source, inparticular an LED, the emergency lighting device comprising: an energystorage unit, a charging circuit to be supplied with a mains supplyvoltage for charging the energy storage unit during a chargingoperation, the charging circuit having potential isolation, and a drivercircuit supplied by the energy storage unit during emergency lightingoperation, for operating the light source, the device further having acontrol unit that is designed to monitor the state of the mains supplyvoltage during the charging operation, and to activate emergencylighting operation upon identifying an emergency state, wherein thecontrol unit determines the state of the mains supply voltage on thebasis of the output voltage of the charging circuit, which outputvoltage charges the energy storage unit, and the charging circuit has acontrollable switch that is activated by the control unit.
 2. Anemergency lighting device according to claim 1, wherein the activationof the switch is effected via an optocoupler.
 3. An emergency lightingdevice according to claim 1, wherein the charging circuit has atransformer.
 4. An emergency lighting device according to claim 3,wherein the charging circuit is constituted by a flyback converter. 5.An emergency lighting device according to claim 4, wherein the controlunit determines the state of the mains supply voltage (U_(in)) takingaccount of a duty cycle for activation of the switch and of the measuredsecondary voltage (U_(flb2)) of the flyback converter.
 6. An emergencylighting device according to any one of claims 1, wherein the controlunit determines the state of the mains supply voltage taking account ofa duty cycle for activation of the switch and of the charging power forthe energy storage unit.
 7. An emergency lighting device according toclaim 6, wherein the control unit determines the charging power for theenergy storage unit through measurement of the current flowing throughthe energy storage unit and of the voltage present at same.
 8. Anemergency lighting device according to claims 5, wherein the controlunit determines the mains supply voltage through comparison of known ormeasured operating quantities with a value table stored in the controlunit.
 9. An emergency lighting device according to claims 1, wherein thedriver circuit is realized as a switching regulator, and has acontrollable switch activated by the control unit.
 10. An emergencylighting device according to claim 9, wherein the control unit activatesthe driver circuit in such a way that the light source is operated witha constant power (P_(led)) or constant current irrespective of the stateof charge of the energy storage unit.
 11. An emergency lighting deviceaccording to claim 10, wherein the control unit determines indirectlythe level of the current supplied to the light source.
 12. An emergencylighting device for operating a light source, in particular an LED, theemergency lighting device comprising: an energy storage unit and adriver circuit supplied by the energy storage unit during emergencylighting operation, for operating the light source, the device furtherhaving a control unit that activates the driver circuit in such a waythat the light source is operated with a constant power or constantcurrent irrespective of the state of charge of the energy storage unit,wherein the control unit, for the purpose of regulating the power,determines indirectly the level of the current supplied to the lightsource.
 13. An emergency lighting device according to claim 11, whereinthe control unit calculates the level of the current supplied to thelight source on the basis of the voltage present at the light source.14. An emergency lighting device according to claim 13, wherein thecontrol unit, in calculating the current supplied to the light source,takes account of the power loss of the driver circuit.
 15. An emergencylighting device according to claim 14, wherein the determination of thepower loss of the driver circuit is effected through comparison ofmeasured operating quantities of the emergency lighting device with avalue table stored in the control unit.
 16. An emergency lighting deviceaccording to claim 14, wherein the control unit, in calculating thecurrent supplied to the light source, further takes account of thesecondary power of the charging circuit or of a charging circuits forthe energy storage unit.
 17. An emergency lighting device according toclaim 16, wherein the determination of the secondary power of thecharging circuit is effected through comparison of measured operatingquantities of the emergency lighting device with a further value tablestored in the control unit.
 18. An emergency lighting device accordingto any one of claims 8, wherein this emergency lighting device has aninterface for receiving external information for programming and/orupdating the value table(s) stored in the control unit.